--Drop perpendiculars from the short base to the long base.
That splits the trapezoid up into a rectangle and two right triangles.
-- The area of a rectangle is (length) x (width).
The area of a triangle is (1/2) (base x height).
-- Apply these area formulas to the three parts of the trapezoid,
addum up, and you'll wind up with
Area = (1/2) (height) (long base + short base)
for the total area of the trapezoid.
